1. Field of the Invention
The invention is directed to a communication process and a communication system with computer-controlled data transfer for controlling the printing process of a printing press.
2. Description of the Prior Art
The course of development in printing technology continues to move away from separate optimization of mechanical and electronic components and increasingly follows the path of improving cooperation between these two divisions. Formerly, the field of printing press electronics could best be summed up as insular, i.e. the press is provided with printing plates, paper, ink and other consumer materials, but does not access existing electronic information and produces a printed product with practically no direct data communications with the outside world. The role of electronics is confined to that of supporting the mechanical components of the printing press. Thus, efforts to achieve better quality, shorter running times or reduction in spoilage, for example, are made by using a greater number of sensors and more intelligent electronics. However, this generally means increased complexity and accordingly an increase in the overall cost of the press.
In a more recent trend of thought, the preparation of the printed image information (in the form of printing plates) is carried out so as to be optimized with respect to the printing press in a process referred to as the preliminary printing stage. This process naturally relies on the acquisition of data concerned with how to proceed with the information subsequently in the printing press so that the modification of information oriented toward the specific printing press can be controlled in order to achieve good results. Naturally, this requires communication between these process divisions.
As a rule, this exchange of data takes place by way of so-called print-run standards which specify a range within which a printing press changes the image data to be printed when using determined grades of ink and paper (e.g., the print-run standard for offset newspaper printing, offset illustration printing or sheet-fed offset printing on coated paper). The preliminary printing stage and the printing press itself must keep within this range. Exceptions are special in-house standards which establish different, more specific transmission characteristics, particularly in the printing of packaging. However, these specialized characteristics are, of course, only valid within the very restricted sphere of operations of the printing house defining them; there are no all-purpose characteristics or acquisition of data not tied to a particular type.
In order to improve printing quality in the sense of better conformity to the original and consistent printing results, it is good policy to allow a flow of information concerning the product to be printed to the regulating means. At the present time, this information is provided almost exclusively by the printer operating the press or by special sensors such as an electronic plate scanner.
Although the product information is available in the preliminary printing stage and is even, in many respects, on a higher level of quality or accuracy than can be made use of by the printer to control the press, this information is generally lost in the output on the printed image substrate. But the control of the printing press could work better with the respective product information from the preliminary stage if this information were requested and received by the press.
Ideas have already be put forth in this direction, for example, in DE 35 27 500 C2 which proposes a new process and a device for presetting ink zones in offset printing. As a rule, the ink zones are adjusted based on ink consumption according to the associated printing areas. In a first approximation, the ink consumption is identical to the surface of the printing form covered with ink, i.e. the printing area. This area coverage can be measured on the finished printing plate by means of a so-called plate scanner. However, given the knowledge of the imposition layout, i.e. the diagram or layout for arranging individual pages with respect to a printing form, it is also possible to calculate the area coverage from the data of the preliminary printing stage. Since the calculation is made from the original data, the measurement error of the plate scanner is eliminated and the accuracy of the values for adjusting the ink zone is increased. The calculated data are sent to the printing press electronics for presetting.
However, another problem consists in that the preliminary stage must recognize specific parameters of the type of printing press in question, since even the zones, for example, differ from one type of printing press to another. Moreover, it is impossible to calculate the ink slider setting in a definitive manner because, on the one hand, the lateral friction which differs depending on the setting of the press is not taken into account and, on the other hand, the transfer characteristics for the transfer of area coverage values to ink slider position values are not known in the preliminary stage.
Further, it is advisable to obtain information for the control of the printing press in general from the data available in the preliminary printing stage. In this regard, European Patent Application EP 0 495 563 A2 proposes the use of an integrated computer-controlled system for controlling a plurality of stages of a printing process in which the information to be applied to the printing plate is in digital form (digital preliminary stage), this system generating, for example, presetting data (inking control) for the printing press and reference values for the inking control based on this layout information, in particular so as to achieve a given printing characteristic. That is, an exchange of data is organized proceeding from the preliminary printing stage.
However, the entire process can only relate to a determined printing press so that all of the specific data relating to the printing press must be known in order to prepare the data. This means that the preliminary stage must be specially adapted to each distinct printing press.